The use of a deflection roll which is arranged between a roll stand and a coiler, and over which a metal strip is passed, is known in the art. Located under the bearings of the deflection roll are force sensors, which measure the bearing forces. The forces acting in the direction of the strip are determined from the bearing force components, and the deflection angle. In the case of small strip tensions, and small deflection angles, the system is severely afflicted by errors, since the measuring errors of the small forces and small deflection angles that are measured lead to considerable errors in the conversion to the strip tension.
It is also known to measure the torque which acts in the drive train between the coiler drum and the motor shaft. A problem arises in this case since the large measuring range of the strip tension is further extended by the possible ratio between maximum and minimum coil radius. Here, too, errors can be great in the case of a small strip tension and a small coil diameter and accuracy requirements come at a high price.
Like other measuring methods, both of the aforesaid methods have several sources of error, which ultimately can lead to measuring errors having an order of magnitude of 1 to 2% in relation to the measuring range end value. In particular in the case of rolling thin-end thicknesses on reversing roll stands (for example foil roll stands), the ratio of maximum to minimum strip tension between the roll stand and the coiler at a stand may be of an order of magnitude of 50. Taking into account the requirement that, even with minimal strip tension, a measuring accuracy of at least 10% of the strip tension at the time must be achieved, the limits of feasible industrial measuring technology are reached, since, if even just tolerable errors are related to the maximum strip tension, or the still higher measuring range end value, the relative measuring error under the conditions can only be of the order of magnitude of 1%.